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Temp2.2 C
RH39 %
WindW 5 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

977
FXHW60 PHFO 222115
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1115 AM HST Sun Jan 22 2017

.SYNOPSIS...
Strong high pressure north of the state will keep windy trades in
place through the day. The trades will diminish tonight and
Monday as a cold front passes by to the north of the state.
Moderate trades will then rebuild across the island chain Tuesday
through Thursday as high pressure sets up to the northeast of the
island chain. A cold front will then approach from the northwest
late in the work week and move through the state next weekend.
Showers will favor windward and mauka areas through the work week,
with more widespread shower activity expected over the upcoming
weekend as a cold front pushes down the island chain.

&&

.DISCUSSION...
Currently at the surface, a 1032 mb high is centered around 750
miles to the north-northeast of Honolulu, with a weakening cold
front just to the south of the Big Island. This is resulting in
windy trades across the island chain this morning. Visible
satellite imagery shows mostly cloudy skies in place in windward
areas, with partly cloudy or mostly sunny conditions in place
across most leeward locales. Meanwhile, radar imagery shows
scattered showers moving into windward areas, with mainly rain
free conditions in leeward locations. Main short term concern for
the rest of the day revolves around wind headlines.

Rest of Today,
Strong trades are expected to continue into the afternoon hours,
with a diminishing trend heading into the evening hours. Wind
observations and high resolution model data suggest that winds
will remain below warning levels, so the High Wind Warning has
been transitioned to a Wind Advisory through 6 pm for most areas.
The one exception is for the area over and downwind of the Kohala
mountains on the Big Island, where winds may gust to 60 mph this
afternoon. As a result the High Wind Warning has been extended
here through 6 pm this evening. As for sensible weather details,
the trades will continue to focus showers over windward and mauka
areas through the afternoon hours, with isolated light showers or
mist reaching leeward areas from time to time due to the strong
trades.

Tonight through Monday night,
High pressure will shift eastward and further away from the state
tonight through Monday night as a cold front passes by well to
the north of the island chain. This will weaken the trade wind
flow across the state, with localized sea breezes and land
breezes possible Monday and Monday night. Most areas should drop
below Wind Advisory levels by this evening, but a few of the
typically windier areas across Maui and the Big Island may see
Wind Advisory conditions continuing through around midnight. As
for sensible weather details, showers will focus primarily over
windward and mauka areas through the period. Some heavier showers
may affect windward sections of Maui and the Big Island tonight
through Monday night as an upper level disturbance moves overhead
and the remnant moisture from the old front lifts northward into
these areas.

Tuesday through Saturday,
Model guidance is in good agreement, showing high pressure
rebuilding north of the state Tuesday through Thursday, allowing
moderate trade winds to become re-established across the island
chain. The trades will then diminish Thursday night through
Saturday as a cold front approaches from the northwest and pushes
into Kauai by late Saturday afternoon. Clouds and showers will
favor windward and mauka areas through the period. The coverage of
showers is expected to remain greatest Tuesday and Tuesday night
particularly over windward sections of Maui and the Big Island
where lingering deep moisture and lower upper level heights will
reside. Drier more stable conditions are expected statewide
Wednesday through Friday night as deep layer ridging builds over
the area. Showers are then expected to increase over the weekend
as another cold front pushes down the island chain.

&&

.AVIATION...
A high pressure center will continue to move eastward away from
the Hawaiian Islands today. Expect strong trade winds to weaken
during the overnight hours. An upper level trough moving eastward
across Kauai and Oahu will bring broken to overcast cirrus clouds
to all islands today. Mostly VFR conditions are forecast today and
tonight with scattered MVFR mainly along windward areas of all
islands and isolated MVFR elsewhere.

AIRMET SIERRA for mountain obscuration over northern and eastern
slopes of Maui and the Big Island remains in effect.

AIRMET TANGO for low level moderate and isolated severe
turbulence south and west of all the Hawaiian Islands remains in
effect. Wind speeds will weaken tonight decreasing turbulence
activity and likely ending this Airmet.


&&

.MARINE...
Generally treacherous conditions continue across the Hawaiian
coastal waters today.

As trade winds have begun to decline from their peak, have
trimmed back the areal extent of the gale warning in the coastal
waters. Expecting these windier waters, South and Southeast of
Oahu, surrounding Maui County and the Big Island, to continue to
experience gale force winds through the day today. Some of these
areas will drop out of the gale area this evening, please refer to
the latest Marine Weather Message, MWWHFO, for further details.
The rest of the coastal waters zones are now covered by a small
craft advisory, which covers both the strong trade winds and the
10 foot plus choppy, wind driven seas which will pose a continuing
hazard into at least early Monday. Windward waters and the
channels will hold the most hazardous conditions for small craft
through the period, and these areas will experience the conditions
for the longest period. The small craft advisory will likely need
to be extended in some areas beyond Monday.

Short period swell energy along the east facing shores will
continue to bring high surf advisory level surf for east facing
shores through Monday afternoon.

A new large northwest swell will likely produce surf well above
the advisory threshold along north and west facing shores of the
smaller islands from Tuesday through Thursday morning. Another
large northwest swell may produce advisory-level surf along north
and west facing shores of the smaller islands starting Friday
night and continuing into next weekend. Otherwise, a minor bump
in surf in south facing shores is possible today due to a small
but long period south swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST this evening for Niihau-Kauai-Oahu-
Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-
Maui Central Valley-Windward Haleakala-Leeward Haleakala-Kona-
South Big Island-Big Island Interior.

High Surf Advisory until midnight HST tonight for Niihau and Lanai.

High Surf Advisory until 6 PM HST Monday for Kauai Windward-Oahu
Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-Big Island North and East.

High Wind Warning until 6 PM HST this evening for Big Island
North and East-Kohala.

Gale Warning until midnight HST tonight for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 PM HST Monday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Big Island Windward Waters.

Gale Warning until 6 PM HST this evening for Oahu Leeward Waters-
Kaiwi Channel-Maui County Windward Waters-Maui County Leeward
Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Bohlin
MARINE...Brenchley

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office